Because of the growth of wireless communications, efforts have been made to increase the amount of wireless frequency spectrum that wireless networks are allowed to use through frequency sharing with incumbent wireless networks. For example, government organizations have recently permitted unlicensed systems broadcasters in their areas of jurisdiction to use portions of wireless spectrum that are officially licensed to television broadcasters in what is called the Television White Space (TVWS). TVWS is defined as unused frequency bands within frequency spectrum licensed for television use. In some geographic regions TVWS also includes frequency spectrum that is registered for use with wireless microphones. The frequency spectrum licensed for television broadcast use is a restricted frequency band but other wireless communications systems may utilize radio channels on available frequencies in the TVWS as long as certain restrictions are observed, such as protections for digital TV receiver signals from interference. The TVWS frequencies/channels permitted to be used are normally ones on which television stations are not currently transmitting. Restrictions may define which TVWS frequencies/channels are permitted for use in a certain geographic area and define a time period during which the frequencies may be used until the restrictions are updated. A wireless network using TVWS spectrum must observe the restrictions as they are updated. For example, most countries maintain one or more TVWS databases associated with a geographic area and maintain the TVWS database to have knowledge of frequencies/channels currently used by television stations in that area. If the operator of a wireless network desires to utilize TVWS spectrum in network operation, the wireless network must periodically check the TVWS database associated with its geographic area/government organization and determine which frequencies/channels it may use for a given time period.
Situations may exist in which the use of TVWS spectrum creates potential interference problems. For example, even though the frequency spectrum licensed for television broadcast use is restricted, a TVWS database responsible for a certain area, such as a country, may not have knowledge of frequency or channels in its TVWS that are being used by one or more television stations outside its area of jurisdiction. For example, a TVWS database of one country may be associated with an area that is near or adjacent to a jurisdictional or international border. In this case television stations beyond the border may cause interference in a wireless network using channels in the TVWS even though the wireless network was given permission to use the frequencies by the TVWS database. Another example of potential interference when using TVWS spectrum is when a wireless network (of multiple wireless networks that are within adjacent or overlapping areas) has queried a TVWS database and begun using channels in the TVWS as permitted by the TVWS database. Since the TVWS database only informs the wireless network of the available TVWS the wireless network may use as regards nonuse by television broadcasters, the wireless network observing the permitted use of the TVWS may be interfered with by the other multiple wireless networks also using the same TVWS spectrum as permitted by the TVWS database. Furthermore, interference affecting TVWS devices in a wireless network can have a cumulative effect because TV stations transmit continuous RF signals.